1. Field of the Invention
The present invention relates to a metal housing used for producing an electronic device such as a notebook computer or a personal digital assistant (PDA).
2. Description of the Related Art
The housing of a mobile electronic device such as a notebook computer or a PDA should meet several requirements. For instance, the housing should be strong enough to carry the incorporated components safely. Also, the housing should have high thermal conductivity for effective cooling of the incorporated components. Further, to be economical with resources, the housing should be made of a material that can be easily recycled. In light of these, the housing of a recent mobile electronic device is often made of metal rather than resin.
Mobile electronic devices, such as notebook computers and PDAs, need to be small in weight and size for convenience of carriage. Producing a lightweight device needs lightweight components. In a mobile electronic device, the metal housing may often occupy more than 30% of the gross weight, and thus it is important to make the housing lightweight for achieving the total weight reduction of the mobile device. Materials suitable for making such a lightweight housing are light metals, such as magnesium (Mg) and aluminum (Al), or light alloys whose main component is one of these light materials. Among the above-mentioned light metals, magnesium is very popular for producing a metal housing because of its high specific tensile strength, effective heat-dissipating nature (which rivals Al) and low specific gravity, which is about 70% of the specific gravity of aluminum.
As known in the art, various manufacturing methods, such as sheet metal forming, die-casting or thixo molding, can be employed to form a metal housing from a lightweight material.
To produce a metal housing by sheet metal forming, use may be made of xe2x80x9cdeep drawingxe2x80x9d in forming e.g. a sidewall of the housing. When employed alone, however, the deep drawing may fail to provide certain shapes necessary for the desired housing. Further, the sheet metal forming does not allow the simultaneous production of a principal housing component (or a main body, to which the incorporated circuits are grounded) and auxiliary parts (bosses, ribs, etc.). To provide a complete housing, the auxiliary parts and the main body need to be prepared separately, and the auxiliary parts should be fixed to the housing body by using e.g. screws. JP-A-5(1993)-49114 and JP-A-10(1998)-107475, for example, disclose such a screw-fixing technique. Unfavorably, the screwing is a time-consuming process, lowering the production efficiency.
The die-casting and the thixo molding, on the other hand, are more efficient methods for producing a metal housing than sheet metal forming. According to them, the auxiliary parts can be formed integral with the main housing body by pouring a molten metal into a die cavity corresponding to the desired shape.
There is, however, a problem in producing a metal housing by die-casting or thixo molding. To provide a lightweight housing, the die cavity should be narrow so that the resultant casting (i.e. the housing) will have as many thin-walled portions as possible. Unfavorably, the narrow space of the die cavity may impede the otherwise smooth flow of the supplied molten metal.
Even if the die cavity has a sufficiently wide passage for the molten metal, the flow-impeding problem can be caused by the complicated inner configurations of the molding die that are designed to provide the auxiliary housing parts (the sidewall portion, the bosses, the ribs, etc.) formed integral with the main housing body. Due to this configuration complexity, the supplied molten metal may not be able to flow smoothly in the cavity. Consequently part of the die cavity may remain to be unfilled with the molten metal, thereby producing a defective metal housing.
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a metal housing that can be produced with less limitations on the configuration design but with a high yield rate.
According to the present invention, there is provided a metal housing including: a housing base made of metal; a first housing component made of metal; and an adhesive that contains metal powder consisting of metal particles. The housing component is fixed to the housing base by the adhesive.
Typically the housing base is a generally flat metal part constituting the upper or lower cover of the product metal housing. The housing base may be prepared by sheet metal forming, which includes shearing, punching, bending, etc. A thin housing base can be made more properly and with a higher yield rate by sheet metal forming than by die-casting, for example.
Preferably, the housing component, such as a sidewall frame, bosses or ribs, may be prepared by die-casting, thixo molding or forging, for example. In particular, the sidewall frame, which is glued to the housing base, can be more easily and with a higher yield rate by die-casting or thixo molding than by sheet metal forming.
Preferably, the metal powder may be made of the same metal as the housing base or the housing component is.
Preferably, the metal powder may have the same composition as the housing base or the housing component does.
Preferably, the metal housing of the present invention may further include a second housing component made of metal and fixed to the housing base by an adhesive that contains metal powder consisting of metal particles. In this instance, the first housing component may be electrically connected to the housing base, while the second housing component may be electrically unconnected to the housing base.
Preferably, the metal particles may be microencapsulated by an insulating resin layer. In this instance, the metal particles in the adhesive for fixing the first housing component to the housing base may be held in direct contact by rupture of the insulating resin layer, so that the first housing component is electrically connected to the housing base.
Preferably, the housing base or the housing component may be made of a metal selected from the group consisting of Mg, Al, Mg alloy and Al alloy.
Preferably, the metal particles may be made of a metal selected from the group consisting of Mg, Al, Mg alloy and Al alloy.
Preferably, the adhesive may contain a resin selected from the group consisting of epoxy resin, acrylic resin and urethane resin.
Preferably, the adhesive may contain a thermoplastic resin such as polyethylene, polypropylene or polystyrene.
Generally, in a conventional notebook computer, a printed circuit board is grounded to the metal housing via an intervening boss or rib, for example. JP-A-7(1995)-221482 discloses such a grounding technique, in accordance with which the circuit board is electrically connected to any portion of the metal housing. However, there may be an occasion where the printed circuit board needs to be connected to one portion of the metal housing (e.g. for grounding purposes), but should not be connected to another portion of the housing (e.g. for avoiding the adverse effect of the electromagnetic field generated in the housing).
The metal housing of the present invention may be composed of a housing base (principal component) and a sidewall frame (auxiliary component) fixed to the housing base, wherein the fixation is achieved by the application of an adhesive that contains conductive metal particles. By controlling the contact (or non-contact) state between the metal particles, it is possible to prevent the sidewall frame from being electrically connected to the housing base. Advantageously, this arrangement allows the printed circuit board grounded to the housing base to be electrically unconnected to the sidewall frame.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.